OwningPtr should impl From<Box<T>>

[dmyyy]

What problem does this solve or what need does it fill?

I am trying to copy the value for a type erased entity component of type &dyn Reflect.

insert_by_id requires an OwningPtr to be passed in. I want to copy the component &dyn Reflect points to and insert the same component for an entity. I can copy the value of &dyn Reflect via clone_value() giving me Box<dyn Reflect>.

There isn't an easy way to get an OwningPtr from a Box. A Box is a unique pointer to some value on the heap - I don't see any reason why it can't be an OwningPtr.

What solution would you like?

implement From<Box<T>> for OwningPtr.

What alternative(s) have you considered?

This can be done with raw pointers.

Additional context

[MrGVSV]

Note that for dyn Reflect we probably want to only do this via the ReflectFromPtr type data.

The reason for this is because a Box<dyn Reflect> might not actually be a Box<T>.

Specifically, when cloning via Reflect::clone_value, you almost always get back a dynamic type (e.g. Box<DynamicStruct>). It would be unsafe to treat the OwningPtr as one that points to T when it really points to DynamicStruct.

So ideally we expose this API through the ReflectFromPtr type data to help ensure these kinds of operations are done safely.

[SkiFire13]

Another reason why this should be avoided is that OwningPtr only owns the data, not the allocation, so the proposed conversion would have to leak the allocation.

I would instead suggest using ReflectComponent to insert a reflected value as component.